1. Technical Field
The present invention relates to a method for producing purine-derived substances such as purine nucleotides purine nucleosides. Purine nucleotides typically include 5′-inosinic acid and 5′-guanylic acid, purine nucleosides typically include inosine and guanosine. Purine nucleosides are important for their use as starting materials for the synthesis of purine nucleotides, and so forth. Bacillus bacteria can be used in the methods described herein. Purine-derived substances are useful as seasonings, drugs, raw materials thereof, and so forth.
2. Background Art
Methods for producing inosine and guanosine by fermentation using adenine auxotrophic strains of Bacillus bacteria have been reported. Derivatives of these bacteria which are made resistant to various drugs such as purine analogues have also been reported (Japanese Patent Publication (KOKOKU) No. 38-23099, Japanese Patent Publication No. 54-17033, Japanese Patent Publication No. 55-2956, Japanese Patent Publication No. 55-45199, Japanese Patent Publication No. 57-14160, Japanese Patent Publication No. 57-41915, Japanese Patent Laid-open (KOKAI) No. 59-42895, and Japanese Patent Laid-open No. 2004-242610). Microorganisms of the genus Brevibacterium have also been reported to be useful for production of inosine and guanosine by fermentation (Japanese Patent Publication No. 51-5075, Japanese Patent Publication No. 58-17592, and Agric. Biol. Chem., 1978, 42, 399-405).
Such mutant strains are typically obtained by treating the microorganism with ultraviolet irradiation or nitrosoguanidine (N-methyl-N′-nitro-N-nitrosoguanidine), and selecting the mutant with the desired properties using a suitable selection medium.
Furthermore, strains which produce purine-derived substances have also been bred using genetic engineering techniques in Bacillus bacteria (Japanese Patent Laid-open No. 58-158197, Japanese Patent Laid-open No. 58-175493, Japanese Patent Laid-open No. 59-28470, Japanese Patent Laid-open No. 60-156388, Japanese Patent Laid-open No. 1-27477, Japanese Patent Laid-open No. 1-174385, Japanese Patent Laid-open No. 3-58787, Japanese Patent Laid-open No. 3-164185, Japanese Patent Laid-open No. 5-84067, and Japanese Patent Laid-open No. 5-192164), Brevibacterium bacteria (Japanese Patent Laid-open No. 63-248394), and Escherichia bacteria (International Patent Publication WO99/03988). Specifically, for example, a method for efficiently producing nucleic acid-derived compounds such as hypoxanthine, uracil, guanine and adenine with a Bacillus bacterium in which the gene (purR) encoding a purine operon repressor is disrupted has been disclosed (U.S. Pat. No. 6,284,495).
In Bacillus subtilis, the purine operon repressor as described above is known to regulate the genes of the purine operon. The purine operon repressor also regulates the purA gene, which is involved in AMP biosynthesis (Proc. Natl. Acad. Sci. USA, 1995, 92, 7455-7459), the glyA gene, which is involved in formyltetrahydrofolic acid biosynthesis (J. Bacteriol., 2001, 183, 6175-6183), the pbuG gene, which encodes the transporter of hypoxanthine/guanine (J. Bacteriol., 2003, 185, 5200-5209), and so forth.
Furthermore, a microorganism which is made auxotrophic for adenine by disruption of the succinyl-AMP synthase gene (purA) and purR genes, and suppression of the decomposition of inosine into hypoxanthine by disruption of the purine nucleoside phosphorylase gene (deoD), has also been reported, as well as a method for producing inosine using this microorganism (see Japanese Patent Laid-open No. 2004-242610).
Transaldolase is one of the enzymes of the pentose phosphate pathway, which catalyzes the reversible reaction which generating D-erythrose-4-phosphate and D-fructose-6-phosphate from sedoheptulose-7-phosphate and D-glyceraldehyde-3-phosphate. There is not much known about the relationship between this enzyme and the biosynthetic pathway of purine-derived substances, and there have been no reports of an attempt to breed bacteria able to produce purine-derived substances by reducing the activity of this enzyme.